assume cs:code, ds:data

data segment
    db 'LoWeR'
    db 'uPpEr'
data ends

code segment
start:
    mov ax, data
    mov ds, ax
    mov bx, 0
    mov cx, 5
foo:
    mov al, 0[bx]
    or al, 00100000b
    mov 0[bx], al
    mov al, 5[bx]
    and al, 11011111b
    mov 5[bx], al
    inc bx
    loop foo
code ends

end start